Method and apparatus for reducing the power consumption of a battery operated transceiver

ABSTRACT

In a method and an apparatus for reducing the power consumption of a battery operated transceiver in standby mode, particularly a mobile telephone station, in which the receiver of the transceiver is adapted to receive successive word blocks on a forward control channel, each word block consisting of a predetermined number of bits forming a dotting sequence, a word synchronization sequence and a predetermined number of word repeats, a switching device is adapted to switch off the receiver after a word repeat in a word block has been validly received, and to switch on the receiver to receive a word repeat in the next successive word block.

TECHNICAL FIELD

This invention relates to a method and an apparatus for reducing thepower consumption of a battery operated transceiver in standby mode,particularly a mobile telephone station, wherein successive word blocksare received by the receiver of the transceiver on a forward controlchannel, each word block consisting of a predetermined number of bitsforming a dotting sequence, a word synchronization sequence and apredetermined number of word repeats.

BACKGROUND

A mobile telephone station in standby mode must monitor the appropriatecontrol channel of the system in which it is located in a manner suchthat the mobile telephone station receives all system control messagesaddressed to it. This necessarily requires that the mobile telephonestation monitors the control channel during any time periods withinwhich control messages directed to that mobile telephone station couldpossibly be transmitted.

In systems such as the EIA/TIA-553 system (AMPS), the Total AcccessCommunications System (TACS), and the D-AMPS IS-136 system, a mobiletelephone station in standby mode, receives successive word blocks on aforward control channel (FOCC). Each word block consists of a 10-bitdotting sequence, an 11-bit word synchronization sequence, and ten wordrepeats each containing 40 bits. The word repeats are separated into twotime-multiplexed data streams, the A stream and the B stream, eachconsisting of five word repeats. Depending on the last digit of thesubscriber number, a mobile telephone station in standby mode listens toeither the A stream or the B stream.

In the above systems, when the mobile telephone station monitors theforward control channel, the receiver is constantly on in that all fiverepeats of a word within a word block, are received, whereupon amajority decision is made, and BCH (Bose-Chaudhuri-Hocquenqhem) decodeoperations and parity check operations are performed. Thus, batterypower is consumed in a mobile telephone station also in the standbymode. Moreover, this power consumption of the receiver of the mobiletelephone station, when the mobile telephone station is monitoring theforward control channel, is a significant percentage of the total powerconsumption of the mobile telephone station.

SUMMARY

The object of the invention is to bring about a method and an apparatusfor reducing the power consumption of a mobile telephone station instandby mode.

This is attained by the method according to the invention in that thereceiver is switched off after a word repeat in a word block has beenvalidly received, and the receiver is switched on to receive a wordrepeat in the next successive word block.

According to the invented method, the receiver is switched on in thattime pulses are generated, said time pulses corresponding to bits thatshould have been received, had the receiver not been switched off, thatsaid time pulses are counted, and that the receiver is switched on whenthe number of time pulses counted corresponds to the number of bitsbetween the end of a word repeat in one word block and the beginning ofa word repeat in the next word block.

According to the invented method, said time pulses are generated by aclock generator in a free-running mode, said clock generator beingbrought into said free-running mode from a tracking mode, in which theclock generator tracks the bits received, when the receiver is switchedoff.

According to the invented method the receiver is switched off after aword repeat in a word block has been validly received, and the receiveris switched on again to receive the same word repeat in the next wordblock.

According to the invented method, the receiver is switched off after thefirst word repeat in a word block has been validly received, and thereceiver is switched on again to receive the first word repeat in thenext word block.

According to the invented method, valid reception of a word repeat isdetermined by performing a parity check of its parity field.

The above object is also attained by the apparatus according to theinvention in that a switching means is adapted to switch off thereceiver after a word repeat in a word block has been validly received,and to switch on the receiver to receive a word repeat in the nextsuccessive word block.

According to the invented apparatus, said switching means is adapted toswitch on said receiver upon receipt of a control signal from a countingmeans, said counting means being adapted to count time pulsescorresponding to bits that should have been received,-had the receivernot been switched off, and to generate the control signal when thenumber of time pulses counted corresponds to the number of bits betweenthe end of a word repeat in one word block and the beginning of a wordrepeat in the next word block.

According to the invented apparatus, a clock generator is adapted, in afree running mode, to generate said time pulses corresponding to bitsthat should have been received, had the receiver not been switched off,and, in a tracking mode, to track the bits received by the receiver,said clock generator being brought into said free running mode from saidtracking mode by said switching means when the receiver is switched off.

According to the invented apparatus, said switching means is adapted toswitch off the receiver after a word repeat in a word block has beenvalidly received, and to switch on the receiver to receive the same wordrepeat in the next word block.

According to the invented apparatus, said switching means is adapted toswitch off the receiver after the first word repeat in a word block hasbeen validly received, and to switch on the receiver to receive thefirst word repeat in the next word block.

According to the invented apparatus, said switching means is adapted todetermine valid reception of a word repeat in a word block by performinga parity check of the parity field of the word repeat.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described more in detail below with reference tothe appended drawings, in which

FIG. 1 illustrates A and B data streams transmitted on an analog forwardcontrol channel in a D-AMPS, AMPS or TACS system,

FIG. 2 is a schematic block diagram of the receiver of a mobiletelephone station, which operates according to the invention,

FIG. 3 is a flow diagram which illustrates steps performed according tothe invention in the receiver according to FIG. 2, and

FIGS. 4a and 4 b are time diagrams illustrating the on and off periodsof a receiver in a mobile telephone station listening to the A datastream and the B data stream, respectively.

DETAILED DESCRIPTION

FIG. 1 illustrates a complete word block 1 and part of a successive wordblock 2, received in standby mode by the receiver of a transceiver,particularly a mobile telephone station, in a D-AMPS, AMPS or TACSsystem.

Each word block consists of a 10-bit dotting sequence DS, an 11-bit wordsynchronization sequence WS, and five word repeats for an A mobiletelephone station and five word repeats for a B mobile telephonestation. Each word repeat contains 40 bits, including a parity field.Whether a mobile station is an A or a B station is determined by thelast digit of the subscriber number.

As indicated in FIG. 1, in word block 1, there are five repeats of wordA1 for a A mobile telephone station, and five repeats of word B1 for a Bmobile telephone station.

In word block 2, only the first repeat of word A2 and the first repeatof word B2 are shown for the A mobile telephone station and the B mobiletelephone station, respectively.

In FIG. 2 which is a schematic block diagram of the receiving portion ofa mobile telephone station, 1 denotes a receiver having an input IN, 2denotes a decoder for decoding the data received by the receiver 1, 3denotes a word synchronization detector, 4 denotes a counter, 5 denotesa clock generator, and 6 denotes a microprocessor.

By means of the flow diagram in FIG. 3 and the time diagrams in FIGS. 4Aand 4B, the operation of the receiving portion in FIG. 2 will now bedescribed.

At Step 300 the process begins in that the power to the receiver 1 isswitched on. At Step 301 the receiver 1 is tuned to a forward controlchannel (FOCC), and at Step 302 the clock generator 5 in FIG. 2 is setto tracking mode. This means that the rate of the time pulses generatedby the clock generator 5 will track the rate of the bits of the incomingword block as decoded by the decoder 2.

At Step 303 word synchronization is performed by means of the wordsynchronization detector 3. The word synchronization is carried out onthe word synchronization sequence WS of a word block, e.g. word block 1in FIG. 1.

At Step 304 repeat 1 of a word of a word block is received, e.g. word A1of word block 1 in FIG. 1. The repeat 1 of word A1 of word block 1 isreceived by the microprocessor 6 from the decoder 2 as indicated by thedoubled-lined arrow in FIG. 2.

At Step 305 the microprocessor 6 performs a BCH decode operation on thereceived repeat 1 of word A1. A BCH decode operation is well known inthis connection and will, consequently, not be described further. AtStep 306, the parity, derived at Step 305 from the parity field of thereceived repeat 1, is checked to verify a correct reception of repeat 1of word A1 of word block 1.

If the parity as checked at Step 306, is OK, at Step 307 the number of“sleep bytes” between the last byte in repeat 1 of word A1 of word block1 and the first byte in repeat 1 of word A2 of word block 2, iscalculated.

At Step 308 the clock generator 5 is set to free running mode, and atthe same time the receiver 1 is switched off at Step 309 by themicroprocessor 6.

Since the receiver 1 is now off, the time pulses gene-rated by the clockgenerator 5 in free running mode correspond to the bits that should havebeen received, had the receiver 1 not been switched off. These timepulses are counted by the counter 4 which informs the microprocessor 6of every counted “sleep byte” at Step 310.

At Step 311 the microprocessor 6 checks whether a “sleep byte” issued bycounter 4 is the last “sleep byte” as calculated at Step 307.

If “YES”, the microprocessor 6 turns on the receiver 1 at Step 312 andat the same time at Step 313 the clock generator 5 is set to trackingmode again to receive repeat 1 of word A2 of word block 2, whereupon theprocess goes back to Step 304 in FIG. 3.

If the parity of repeat 1 of word A2 of word block 2 is OK as checked atStep 306, the receiver 1 will again be switched off at Step 309.

Thus, as apparent from FIG. 4a, the receiver 1 in an A mobile telephonestation will be on only during repeat 1 of a word A in each word block.The same is true for a B mobile telephone station which will be on onlyduring repeat 1 of a word B in each word block. Consequently, the powerreduction effect is equal for both A and B mobile telephone stations.

If, at Step 306, the parity of repeat 1 of a word in a word block, isnot OK, the rest of the repeats of that word in the word block, isreceived at Step 314, whereupon at Step 315 a word synchronization hasto be performed again by means of the word synchronization detector 3.

At Step 314, when the rest of the repeats of the same word have beenreceived, a majority decision is made and BCH decode operations andparity check operations are performed in a conventional manner.

After that the word synchronization has been performed at Step 315,repeat 1 of a word of the successive word block is received at Step 304and the process goes on as described above.

In accordance with the invention, the sleep time is prolonged over theend of a current word block and the bit and word synchronizationsequences of the following word block, i.e. the receiver 1 is switchedon exactly in time for receiving the first word repeat in the successiveword block. Thus, the sleep time equals the maximal theoretical onebetween equal-numbered word repeats in two successive word blocks.

By means of the invention, the resynchronization to the received datastream, after tuning to a forward control channel and initial use of theword synchronization sequence, is avoided. This minimizes the risk offalse word synchronization detection after the sleep periods, whichcould occur if the sleep time was different from the one describedabove.

At Step 304 in FIG. 3, it is not absolutely necessary to receive thefirst repeat of-a word of a word block and carry out the rest of theprocess in relation to that first repeat. In fact, it is theoreticallypossible to select any of the five repeats at Step 304 to be receivedand run through the process on the basis on that selected repeat.However, if at Step 306 it is found that the parity of the selectedreceived repeat is not OK, too little data may be received at Step 314to make a majority decision. Thus, in practice, the first repeat of aword of a word block should be received.

Also, at Step 306, if the parity of the first word repeat is found to benot OK, at Step 314 just the second repeat could be received instead ofall the repeats 2-5. In that case the BCH decode operation at Step 305would have to be performed on that second repeat. If the parity aschecked at Step 306 is found to be OK for that second repeat, theprocess would continue at Step 307 by calculating the number of “sleepbytes” from that second repeat to the first repeat in the nextsuccessive word block.

What is claimed is:
 1. A method for reducing the power consumption of abattery operated transceiver in standby mode, particularly a mobiletelephone station, wherein successive word blocks are received by areceiver of the transceiver on a forward control channel, each wordblock consisting of a predetermined number of bits forming a dottingsequence, a word synchronization sequence and a predetermined number ofword repeats, comprising the steps of switching off the receiver after arespective word repeat in a current word block has been validlyreceived, and switching on the receiver to receive a corresponding wordrepeat in a next successive word block, wherein the receiver is switchedon when a number of time pulses counted corresponds to a number of bitsbetween an end of the respective word repeat in the current word blockand a beginning of the corresponding word repeat in the next word block,wherein the time pulses correspond to bits that should have beenreceived, had the receiver not been switched off, and the time pulsesare generated by a clock generator in a free-running mode, said clockgenerator being brought into said free-running mode from a trackingmode, in which the clock generator tracks the bits received, when thereceiver is switched off.
 2. A method as claimed in claim 1, wherein thereceiver is switched off after the respective word repeat in the currentword block has been validly received, and the receiver is switched onagain to receive a same word repeat in the next word block.
 3. A methodas claimed in claim 2, wherein the receiver is switched off after afirst word repeat in the current word block has been validly received,and the receiver is switched on again to receive a first word repeat inthe next word block.
 4. A method as claimed in claim 1, wherein validreception of each word repeat is determined by performing a parity checkof its parity field.
 5. An apparatus for reducing the power consumptionof a battery operated transceiver in standby mode, particularly a mobiletelephone station, wherein a receiver of the transceiver receivessuccessive word blocks on a forward control channel, each word blockconsisting of a predetermined number of bits forming a dotting sequence,a word synchronization sequence and a predetermined number of wordrepeats, comprising a switching device that switches off the receiverafter a respective word repeat in a current word block has been validlyreceived, and switches on the receiver to receive a corresponding wordrepeat in the next successive word block, and a clock generator that ina free running mode, generates time pulses corresponding to bits thatshould have been received, had the receiver not been switched off, and,in a tracking mode, tracks the bits received by the receiver, said clockgenerator being brought into said free running mode from said trackingmode by said switching device when the receiver is switched off, whereinthe switching device switches on said receiver upon receipt of a controlsignal from a counting means, said counting means counting the timepulses corresponding to bits that should have been received, had thereceiver not been switched off, and generating the control signal whenthe number of time pulses counted corresponds to the number of bitsbetween the end of the respective word repeat in the current word blockand a beginning of the corresponding word repeat in the next word block.6. An apparatus as claimed in claim 5, wherein the switching deviceswitches off the receiver after the respective word repeat in thecurrent word block has been validly received, and switches on thereceiver to receive a same word repeat in the next word block.
 7. Anapparatus as claimed in claim 6, wherein the switching device switchesoff the receiver after a first word repeat in the current word block hasbeen validly received, and switches on the receiver to receive a firstword repeat in the next word block.
 8. An apparatus as claimed in claim5, wherein the switching device determines valid reception of each wordrepeat in each word block by performing a parity check of the parityfield of the word repeat.